(1) Field of the Invention
The present invention relates to a gas duct having a honeycomb structure, used mainly in an automobile exhaust gas purification system.
(2) Description of Related Art
Currently, gas ducts with honeycomb structure are in extensive use because they have low pressure loss (when a gas is passed therethrough) owing to their high open frontal area, and the structures show an excellent exhaust gas purifiability. As an example of such gas ducts, a widely known ceramic honeycomb catalytic converters are used in exhaust gas purification systems for automobiles.
To produce such a ceramic honeycomb catalytic converter, a ceramic honeycomb catalyst is held in a converter casing (this operation is called xe2x80x9ccanningxe2x80x9d) for easy handling of the honeycomb catalyst.
For example, as shown in FIGS. 4(a) and 4(b), in order to reliably hold a honeycomb catalyst 12 in a metal case 11 and further lessen the impact applied to the catalyst 12 from outside, a ceramic fiber mat 13 is inserted, under pressure, between the outer surface of the honeycomb catalyst 12 and the inner surface of the metal case 11, after which the honeycomb catalyst 12 is held in the metal case 11 in the axial direction of the metal case 11. Specifically, a hook 14, which is fitted to one end of the metal case 11 and projects toward the center of a circle formed by the one end of the metal case 11, and a retainer ring 15 welded to the other end of the metal case 11 or a plurality of projections 16 (see FIGS. 5(a) and 5(b)) extending from the other end of the metal case 11, but bent towards the center of a circle formed by the other end of the metal case 11, are allowed to abut on the honeycomb catalyst 12; then, each one cone (not shown), which is a metal member enabling easier incoming and discharging of exhaust gas, is fitted to the both ends of the metal case 11 by welding, or the like.
When the honeycomb catalyst 12 is held in the metal case 11 as above, however, the hook 14 and the retainer ring 15 both fitted to the metal case 11 block part of the passages of the honeycomb catalyst 12, which makes impossible the effective utilization of the whole volume of the honeycomb catalyst 12, and moreover incurs an increase in pressure loss. This leads to an increase in emission or a reduction in engine performance when the metal case 11 holding the honeycomb catalyst 12 is used as a honeycomb catalytic converter.
Further, since the hook 14 and the retainer ring 15 are fitted to the metal case 11, there arises an increase in processing cost and material cost of honeycomb catalytic converter.
In order to alleviate the above-mentioned problems of the related art, the present invention aims at providing a gas duct having a honeycomb structure, which utilizes the whole volume of the honeycomb structure, which is lower in pressure loss, and which is lower in cost.
According to the present invention, there is provided a gas duct having a honeycomb structure, which comprises:
a metal case,
a honeycomb structure accommodated in the metal case,
a holding member placed between the outer surface of the honeycomb structure and the inner surface of the metal case, and
a cone(s) fitted to the inner surface of the metal case at one or both openings of the metal case, wherein the circumference(s) of one or both end faces of the honeycomb structure is (are) allowed to abut on the cone(s).
In the gas duct comprising a honeycomb structure, of the present invention, it is preferable that the circumference(s) of the end face(s) of the honeycomb structure abuts (abut) on the cone(s) at an angle of 45xc2x0 to 85xc2x0.
In the gas duct having a honeycomb structure, of the present invention, it is also preferable that the circumference(s) of the end face(s) of the honeycomb structure is (are) chamfered and the size or radius of chamfering is 0.1 to 1 mm.
The gas duct having a honeycomb structure, of the present invention preferably takes the following form:
the honeycomb structure is made of a ceramic or a metal, and is a catalyst for exhaust gas purification, a filter for capturing the particulate substances present in exhaust gas, or a heat exchanger;
the holding member is a ceramic fiber mat or a metal-made wire mesh; and
the metal case has a stuffing structure, a tourniquet structure, or a clam-shell structure.